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American locomotives


At one point in the history of the locomotive, American models began to drift away from the English type. In America it was impracticable, because of the cost, to build roads on the basis of the English railways. Physical conditions made it impossible to obtain the wide curves or the substantial road beds of the British lines.

To overcome the shortness of the American curves, the first step was the movable trucks of the South Carolina. A year later, John B. Jervis designed and patented a locomotive that did away with the rigid wheel base of the British engines. With their fixed bases, the imported locomotives rapidly broke up the light American rails and racked themselves to pieces. Jervis' engine in a measure overcame this. It had a set of fixed driving wheels, with a forward truck capable of moving through a wide are. It turned sharp curves with ease, and since 1834 this principle has been applied to all rolling stock in America.

In England the cylinders, piston, and connecting rods, the valve gear, and other parts of the machinery, were drawn inside the wheel base. In America they were kept outside, and they still remain there.

Another stride was made in 1836, when Henry R. Campbell, of Philadelphia, patented the use of two pairs of driving wheels coupled by rods, a combination lateron almost universally adopted, and known as the American type of locomotive.

In England, where distances are comparatively short, railways are built in the most substantial manner, running in straight lines or wide curves, with masonry, costly bridges, stone viaducts, and tunnels or deep cuts at every large obstruction. But when one considers the cost that such engineering would involve in America, it call be understood why the U.S. railroads have followed lines of their own. It was absolutely necessary to overcome this difference, and so we have developed special, distinct types of locomotives and other rolling stock.

In Europe Stephenson's locomotive has hardly changed, except in detail. It had increased in weight and power, in perfection of material, but its appearance was virtually the same as it was sixty years ago.

In the U.S. they had to climb stiff grades, and go tremendous distances. They couldn't lay masonry for three thousand miles, nor couldn't they tunnel or cut into every slight rise. So they were compelled to build engines that would turn almost on themselves, climb heavy grades, and do stiff work, in the same time. Almoreover, they had to develop special engines for nearly every class of work.

The successive steps in the development of the locomotive were slow and gradual. The invention of the coupled drivers and a forward truck was one of the first conspicuous movements. Jervis' swiveling truck was, when it came into general use, a still greater stride. It enabled American engineers to build lines far less expensive than the English roads, for with the swiveling truck the locomotives were capable of getting over track that would have been impassable to English engines.

Lateron, the British companies are using this truck, and were embodying many other American ideas in their locomotive machinery. An important development following close upon the swiveling truck was the invention of the equalizing beam for engine springs. The first English engines used here were constantly leaving the iron, a fault due to their rigid wheel base and consequent uneven, jumpy action. To overcome this, Joseph Harrison, Jr., of Philadelphia, invented this spring beam.

Superficially, this is a bar connecting the springs on which the Journals of the drivers bear. Where there is a pair of springs on each side of the engine, each pair is joined on the inner end by a level resting, at its center, on a fulcrum.

Thus, when the weight is unevenly divided on one wheel and its spring, it tips the equalizing beam, and distributes the weight evenly to the other spring. In this way vertical flexibility is obtained, as well as an even distrihution of weight to all the wheels, by which adhesion of the drivers is assured. American locomotives were consequently able to draw heavier loads than their English rivals of the same weight and nominal power - though in England this was stoutly denied.

Still another advantage was that, owing to their flexibility, American locomotives are better able to withstand shocks, sudden jolts and blows, a feature that enabled them to do longer and harder work without injury.